l would say that only my mint restored titles: IJ, MB & TAFG are lifers. My clan all really love these games.
I had initially thought some of my Sterns (ie: MET/TWD) would never leave; but due to limited space and so many great new pins, I've had to trade some.
As others have alluded to, having limited space is one of the main reasons.
I also figure, I will always be able to re-purchase most of the Stern titles; whereas finding collector grade examples of my B/W titles is near impossible to locate locally.